Thermally enhanced ultrasound transducer system

ABSTRACT

A system and method for removing unwanted heat generated by a piezoelectric element of an ultrasound transducer. Some implementations have high thermal conductivity (HTC) material placed adjacent to the piezoelectric element. The HTC material can be thermally coupled to one or more heat sinks. Use of HTC material in conjunction with these piezoelectric element surfaces is managed to avoid degradation of propagating acoustic energy. Use of the HTC material in conjunction with heat sinks allows for creation of thermal paths away from the piezoelectric element. Active cooling of the heat sinks with water or air can further draw heat from the piezoelectric element. Further implementations form a composite matrix of thermally conductive material or interleave thermally conductive layers with piezoelectric material.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority benefit of provisional application Ser.No. 60/700,772 filed Jul. 20, 2005.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is directed to ultrasound transducers for medicalapplications.

2. Description of the Related Art

Conventional ultrasound transducers used for medical applications, suchas High Intensity Focused Ultrasound (HIFU), generate unwanted heat thatcan affect performance of the transducer. This unwanted heat is due topiezoelectric elements, used therein, having some inefficiency inconverting electrical power into acoustic waves. Ceramic piezoelectricelements typically have low thermal conductivity (such as approximatelyone to two W/mC), which contributes in part to the unwanted heatproducing undesirable elevated temperatures.

Some medical and other applications require transducer temperatures tobe kept in narrow ranges. For example, when transducers are near ortouching biological tissue not intended for treatment, the dosage forthis untreated tissue must be held below an equivalent thermal dose of43 degrees centigrade for 60 minutes. For temperatures above 43 degreescentigrade, equivalent thermal dose is proportional to approximately2**(T-43), where T is temperature in degrees centigrade. For example, anequivalent thermal dose will also occur at 44 degrees centigrade forapproximately 30 minutes and at 50 degrees centigrade for approximately30 seconds. If a transducer does not come into contact with a patient,generally higher temperatures are permitted, however, temperature levelsin excess of 80 or 90 degrees centigrade are most likely to result indamage to the transducer and/or portions of electrical and/or mechanicalelements supporting or otherwise associated with the transducer.

For instance, HIFU treatments can involve tens or hundreds of Watts offocused acoustic power resulting in acoustic intensities from 1,000 to40,000 watts per square centimeter (although typical values are on theorder of 2,000 W/cm²); these values can be compared with a fewmilliwatts per square centimeter for typical diagnostic ultrasoundapplications. The HIFU treatments can include sound frequencies from onehundred kilohertz to over ten megahertz, with the most common range of1-10 MHZ.

Conventional attempts at improving performance and lessening otherunwanted effects include improving performance so less heat isgenerated, compensation through electronic controls and/or attempts atremoving generated heat. Unfortunately, conventional approaches can lackeffectiveness, be cumbersome and/or degrade performance.

A conventional first ultrasound transducer 10, as schematically depictedin FIG. 1 as having elements positioned along an illustrativeX-dimension (with a depicted illustrative Y-dimension normal to theX-dimension) to include a rear medium 12, such as air, adjacent to afirst piezoelectric element 14, such as a ceramic material, adjacent toa front layer 16. Air is generally useful for the rear medium since itacts as a near perfect reflector in cases where the acoustic impedanceof the piezoelectric element 14 is much different than that of air(approximately 0.0004 MRayls). In operation, the front layer 16 isplaced adjacent to a front medium 18, such as a tissue of a recipient ofultrasound 20.

The piezoelectric element 14 converts electrical energy into theultrasound 20, which conducts through the front layer 16 into the frontmedium 18. The front layer 16 is typically fashioned to help match theacoustical impedance between the piezoelectric element 14 and the frontmedium 18 for better transfer of the ultrasound 20 from thepiezoelectric element to the front medium. For impedance matching, thefront layer 16 can be typically as thick as approximately one or moremultiples (in particular implementations, odd multiples) of a quarterwavelength of an ultrasound frequency used in operation such as a centeroperational frequency. The front layer 16 would also have an acousticimpedance to help match impedances of the piezoelectric element 14(having an acoustic impedance such as approximately 30-35 MRayls) andthe front medium 18 (for instance, tissue has an acoustic impedanceapproximately 1.6 MRayls). The acoustic impedance of single matchinglayers, such as the front layer 16, can be typically chosen to be withinthe range of 4 to 8 MRayls. The thermal conductivity of a matching layerin a conventional transducer is often in the range of 1 to 3 W/mC, whichis typically the result of loading an epoxy matrix with a higheracoustic impedance and lower acoustic attenuation material such assilicon dioxide or aluminum oxide powder.

Generally, an acoustic impedance for the front layer 16 somewherebetween that of the piezoelectric element 14 and that of the frontmedium 18 is used for acoustic impedance matching of the piezoelectricelement and the front medium. Unfortunately, materials used for acousticimpedance matching tend to give conventional matching layers such as thefront layer 16 low thermal conductivity. For the front layer 16 betweenthe piezoelectric element 14 having an acoustic impedance Z_(c) and thefront medium having an acoustic impedance Z_(t), the impedance of thefront layer 16 can be approximated to be between (Z_(c)Z_(t))^(1/2) and(Z_(c)Z_(t) ²)^(1/3). For example, for a ceramic impedance of 34 MRayls(for the piezoelectric element 14) and tissue at 1.6 MRayls (for thefront medium 18), then it would be desirable for a single quarter wavelayer to have an acoustic impedance in the range 4-10 Mrayls.

The front layer 16 can also serve to electrically insulate and/orphysically protect the piezoelectric element 14 from physical wear ordamage. In some applications, the front layer 16 is also shaped toprovide an acoustic lens function to focus ultrasound.

A first implementation of the first conventional ultrasound transducer10 is shown in FIG. 2 and FIG. 3 to include a housing 22 to enclosecomponents enumerated above. With the first implementation, thepiezoelectric element 14 and the front layer 16 are formed andoptionally adjusted to project the ultrasound 20 to have a focal point24 located a desired distance into the front medium 18.

As part of the conversion by the piezoelectric element 14 of electricalenergy into ultrasound 20, unwanted heat, as mentioned above, isgenerated by the piezoelectric element. Electronic compensation can beused with the first conventional ultrasound transducer 10 to helppartially mitigate effects of the unwanted heat on performance of thefirst conventional ultrasound transducer.

A second conventional ultrasound transducer 30 is schematically depictedin FIG. 4 to include a thermal heat sink 32 positioned adjacent to thefront layer 16 so that in operation the thermal heat sink is adjacent tothe front medium 18 as shown. The thermal heat sink 32 is used to removeheat from the vicinity of the piezoelectric element 14 and is fashionedto conduct the ultrasound 20. Unfortunately, in practice the thermalheat sink 32 can be very thick compared with the front layer 16 alongthe X-dimension of travel of the ultrasound 20 so can also dissipatesignificant portions of the ultrasound 20 thereby resulting in more heatbeing generated and reducing efficiency with the transducer performance.The thermal heat sink 32 can also have other operational issues due toits added size and possible use of fluid, such as water, as at least aportion of the thermal mass.

A first implementation of the second conventional ultrasound transducer30 is shown in FIG. 5 as using a fluid, such as water, for the thermalheat sink 32, which is shown to be contained by a structural appendage34 and an acoustic membrane 36. Water can serve a dual purpose to cooland also acoustically couple between the second conventional ultrasoundtransducer 30 and a target. A second implementation of the secondconventional ultrasound transducer 30 is shown in FIG. 6 to include asolid, such as a metal, for the thermal heat sink 32. In this secondimplementation, the structural appendage 34 includes channels 38 for afluid, such as water, to be passed through to aid in removal of heat.Associated with these first and second implementations of the secondconventional ultrasound transducer 30, the use of fluid, additionalmass, attenuation of desired ultrasound energy, and positioning of thethermal heat sink 32 and the structural appendage 34 can raiseoperational issues.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

FIG. 1 is a schematic diagram of a first conventional ultrasoundtransducer.

FIG. 2 is a sectional perspective view of a first implementation of thefirst conventional ultrasound transducer of FIG. 1.

FIG. 3 is a sectional elevation view of the first implementation of thefirst conventional ultrasound transducer shown in FIG. 2.

FIG. 4 is a schematic diagram of a second conventional ultrasoundtransducer.

FIG. 5 is a sectional elevation view of a first implementation of thesecond conventional ultrasound transducer of FIG. 4.

FIG. 6 is a sectional elevation view of a second implementation of thesecond conventional ultrasound transducer of FIG. 4.

FIG. 7 is a schematic diagram of a first implementation of a thermallyenhanced ultrasound transducer.

FIG. 8 is a sectional elevation view of a first variation of the firstimplementation of the thermally enhanced ultrasound transducer shown inFIG. 7.

FIG. 9 is a schematic diagram of a second implementation of thethermally enhanced ultrasound transducer.

FIG. 10 is a sectional perspective view of a first variation of thesecond implementation of the thermally enhanced ultrasound transducershown in FIG. 9.

FIG. 11 is a sectional perspective view of a second variation of thesecond implementation of the thermally enhanced ultrasound transducershown in FIG. 9.

FIG. 12 is a sectional perspective view of a third variation of thesecond implementation of the thermally enhanced ultrasound transducershown in FIG. 9.

FIG. 13 is a schematic diagram of a third implementation of thethermally enhanced ultrasound transducer.

FIG. 14 is a sectional perspective view of a first variation of thethird implementation of the thermally enhanced ultrasound transducershown in FIG. 13.

FIG. 15 is a schematic diagram of a fourth implementation of thethermally enhanced ultrasound transducer.

FIG. 16 is a schematic diagram of a fifth implementation of thethermally enhanced ultrasound transducer.

FIG. 17 is a schematic diagram of a first version of the front highthermal conductivity (HTC) section of the thermally enhanced ultrasoundtransducer.

FIG. 18 is a sectional perspective view of a first variation of thefifth implementation of the thermally enhanced ultrasound transducerusing the first version of the front HTC section.

FIG. 19 is a schematic diagram of a second version of the front highthermal conductivity (HTC) section of the thermally enhanced ultrasoundtransducer.

FIG. 20 is a sectional perspective view of a second variation of thefifth implementation of the thermally enhanced ultrasound transducerusing the second version of the front HTC section.

FIG. 21 is a schematic diagram of a third version of the front highthermal conductivity (HTC) section of the thermally enhanced ultrasoundtransducer.

FIG. 22 is sectional perspective view at a third variation of the fifthimplementation of the thermally enhanced ultrasound transducer using thethird version of the front HTC section.

FIG. 23 is a schematic diagram of a fourth version of the front highthermal conductivity (HTC) section of the thermally enhanced ultrasoundtransducer.

FIG. 24 is a schematic diagram of a fifth version of the front highthermal conductivity (HTC) section of the thermally enhanced ultrasoundtransducer.

FIG. 25 is sectional perspective view at a fourth variation of the fifthimplementation of the thermally enhanced ultrasound transducer using thefifth version of the front HTC section.

FIG. 26 is a sectional perspective view of a first high thermalconductivity (HTC) implementation of the piezoelectric element used inthe thermally enhanced ultrasound transducer.

FIG. 27 is a sectional perspective view of a second HTC implementationof the piezoelectric element used in the thermally enhanced ultrasoundtransducer.

FIG. 28 is a sectional perspective view of a sixth implementation of thethermally enhanced ultrasound transducer using a third HTCimplementation of the piezoelectric element of FIG. 27.

FIG. 29 is a sectional perspective view of a seventh implementation ofthe thermally enhanced ultrasound transducer using a fourth HTCimplementation of the piezoelectric element.

FIG. 30 is a perspective view of a first conventional compositeimplementation of the piezoelectric element.

FIG. 31 is a perspective view of a second conventional compositeimplementation of the piezoelectric element.

FIG. 32 is a perspective view of a fifth HTC implementation of thepiezoelectric element.

FIG. 33 is a perspective view of a sixth HTC implementation of thepiezoelectric element.

FIG. 34 is a schematic diagram of a monolithic HTC implementation of thepiezoelectric element.

FIG. 35 is a schematic diagram of a monolithic HTC implementation of apiezoelectric material.

FIG. 36 is a schematic diagram of a monolithic HTC implementation of afirst piezoelectric member.

FIG. 37 is a schematic diagram of a monolithic HTC implementation of asecond piezoelectric member.

DETAILED DESCRIPTION OF THE INVENTION

A system and method for removing unwanted heat generated by apiezoelectric element of an ultrasound transducer while maintainingtransducer efficiencies is disclosed herein. In some implementations,relatively small amounts of high thermal conductivity (HTC) material areplaced in juxtaposition with the piezoelectric element on front and/orback surfaces of the piezoelectric element. Generally HTC materials havea thermal conductivity of over 100 W/mC. Some HTC materials can includemetals and other materials of high thermal conductivity (for instance,aluminum at approximately 205-237 W/mC, copper at approximately 385-401W/mC, gold at approximately 314-318 W/mC, silver at 406-429 W/mC, brassat approximately 109-159 W/mC, impure diamond at approximately 1,000W/mC, and purified synthetic diamond at approximately 2,000-2,500 W/mCthermal conductivity).

The HTC material can be thermally coupled to one or more heat sinks,which can be integrated with the ultrasound transducer, such as ahousing or other structure, and positioned out of the path of ultrasoundgenerated by the piezoelectric element. The typically large surface areaversus thickness of the piezoelectric element (for instance, someapplications having 50:1 to 100:1) is also used in placement of the HTCmaterial. Use of HTC material in conjunction with these piezoelectricelement surfaces is managed to avoid degradation of acoustic energypropagating forward into to a front medium, such as tissue, and tominimize acoustic energy loss through a rear medium.

Piezoelectric ceramic used in HIFU and other transducers is typicallycoated with a thin (generally less than 10% of an operational ultrasoundwavelength) electrically conductive layer to serve as electrodes. Thismaterial is also thermally conductive but is purposely relatively thinso that it will have minimal effect on acoustic performance. The presentimplementations use significantly thicker layers for the HTC materialthan is typically used for the thin electrically conductive material butnot in excess as to degrade transducer efficiency.

Piezoelectric ceramic elements are typically coated with high electricalconductivity material to serve as electrodes on opposite sides of theceramic. Although the electrode material layer may also have highthermal conductivity, the electrode layer is typically relatively thin,on the order of a few microns, and therefore is limited in its functionto transfer heat laterally to a surrounding heatsink. As can be seen inthe following equation, the rate of heat transfer by conduction (ΔQ/Δt)is a function of the cross section area of the material, A.$\frac{\Delta\quad Q}{\Delta\quad t} = \frac{{kA}\quad\Delta\quad T}{d}$

where

ΔT=temperature difference

d=length

A=cross-sectional area

k=material thermal conductivity

It is preferable to utilize the high thermal conductivity of theelectrode layers to conduct heat from the piezoelectric ceramic directlyforward and/or backward (in the direction of large cross section area)and into HTC matching layers, such as aluminum. The HTC matching layershave a relatively large cross section area in the lateral directiontoward the thermally conductive housing/heatsink due to a thickness thatmay be 10 to 100 times greater than the electrode thickness.

Use of the HTC material in conjunction with heat sinks allows forcreation of thermal paths away from the piezoelectric element so that athermal gradient is maintained across the span of HTC material andcoupled heat sinks. Active cooling of the heat sinks with water or aircan further help maintain thermal gradients to draw heat from thepiezoelectric element. Various applications include continuous run timesof several minutes (with a minimum of at least a few seconds) in whichhigh levels of ultrasound are generated and transmitted into targettissue without significant loss of acoustic energy and without thermaldamage to associated equipment or thermal based injury occurring. Insome cases, it is desirable to utilize a transducer of relatively smallsize, driven at a relatively high acoustic power; which makes furtherdemands on the thermal management of the transducer system.

Further implementations improve the thermal conductivity of thepiezoelectric element itself by forming a composite matrix of thermallyconductive material or by interleaving the ceramic with thermallyconductive layers. Increased thermal conductivity of the piezoelectricelement helps to move thermal energy toward outside edges and/or frontand back surfaces.

A first implementation of a thermally enhanced ultrasound transducer 100is shown in FIG. 7 to include a rear medium 101, such as air, positionedadjacent to a rear high thermal conductivity (HTC) layer 102. Incontrast, if the rear medium 101 is water rather than the air, thereflected wave is reduced to approximately 84%, which can beunacceptable for some applications. In general, a member, a layer, amaterial, an element, a section, or other portion of the thermallyenhanced ultrasound transducer 100 designated herein as “high thermalconductivity (HTC),” the thermal conductivity of such portion issubstantially similar or higher than metals such as aluminum unless suchportion is formed as a composite such as a polymer with metal powder asfurther described below.

It is desired that negligibly small amounts of acoustic energy should beabsorbed by the rear HTC layer 102 and thus low acoustic absorptionmaterials such as a metal, which also has a high thermal conductivity,is most desirable. In turn, the rear HTC layer 102 is positioned injuxtaposition with a piezoelectric element 104, which is positioned injuxtaposition with a front high thermal conductivity (HTC) section 106.The piezoelectric element 104 is shown in FIG. 7 to be positionedbetween and adjacent to electrode material 104 a, which is adjacent tothe rear HTC layer 102 and the front HTC section 106. The electrodematerial 104 a is typically a few microns thick of electricallyconductive material. Because the electrode material 104 a iselectrically conductive, the electrode material is also thermallyconductive. The electrode material 104 a is made purposely thin such astypically small fractions of a wavelength so that there will be minimaleffect on the acoustic performance.

In contrast, with 4 MHz resonance frequency ultrasound production, therear HTC layer 102 has a thickness in the range of hundreds of micronsas determined by the particular resonance frequency being used andwithout significantly degrading transducer efficiency. The piezoelectricelement 104 can be made from ceramics such as lead titanates and leadzirconate titanates or other materials that have a piezoelectric effect.

The piezoelectric element 104 generates forward ultrasound 107 a andrearward ultrasound 107 b. Due to the discontinuity between the rearmedium 101 and the layer in juxtaposition (the rear HTC layer 102 asdepicted in FIG. 7 or the piezoelectric element 104 in otherimplementations), a portion of the rearward ultrasound 107 b reversesdirection as reflected ultrasound 107 c to add constructively with theforward ultrasound 107 a as combined ultrasound 107. In implementationsthe rear medium 101 can typically be comprised of air so that nearly allof the rearward ultrasound 107 b reverses direction as the reflected 107c due to a large difference between acoustic impedances between the rearmedium 101 and the layer in juxtaposition (the rear HTC layer 102 asdepicted in FIG. 7 or the piezoelectric element 104 in otherimplementations).

The polarity of the reflected ultrasound 107 c depends upon the relativeacoustic impedances of the rear medium 101 and the layer injuxtaposition (the rear HTC layer 102 as depicted in FIG. 7 or thepiezoelectric element 104 in other implementations). If the acousticimpedance of the rear medium 101 is low (such as for air) relative tothe acoustic impedance of the layer in juxtaposition, which has arelatively high acoustic impedance (such as aluminum for the rear HTClayer 102 depicted in FIG. 7 or ceramic for the piezoelectric element104 for other implementations), then the reflected ultrasound 107 c willhave opposite polarity than the rearward ultrasound 107 b. As a resultthe reflected ultrasound 107 c will travel back toward the piezoelectricelement in phase and will interfere constructively with forwardultrasound 107 a as both the forward ultrasound 107 a and the reflectedultrasound 107 c will propagate to the front medium 18 is a desiredconfiguration such as a HIFU beam. Conversely, the reflected ultrasound107 c has the same polarity as the rearward ultrasound 107 b if theacoustic impedance of the rear medium 101 is high relative to the layerin juxtaposition.

In an implementation, the rearward ultrasound 107 b propagates firstfrom the piezoelectric element 104 through the rear HTC layer 102 madefrom aluminum to the rear medium 101 comprised of air. A reflectioncoefficient can be calculated at the boundary between air and the topside of an aluminum version of the rear HTC layer 102 by substituting Z₂for the impedance of air (0.000411 MRayls) and Z₁ for aluminum (17.1MRayls) in equation (1) as shown in equation (2) as follows:$\begin{matrix}{r = {\frac{{411*10^{- 6}} - 17.1}{{411*10^{- 6}} + 17.1} \cong {- 1.0}}} & (2)\end{matrix}$Showing that reflection of the rearward ultrasound 107 b can be close tocomplete.

Implementations include thicknesses dependent upon the selectedoperational frequency such as the nominal center ultrasound frequencyfor the rear HTC layer 102 of one or more multiples of approximately onehalf wavelength at the nominal center ultrasound frequency (for example,approximately 0.8 mm for a nominal center frequency of 4 MHz). Inimplementations constructive reflection of the rearward ultrasound 107 bis attained if the rear HTC layer 102 is a single or a multiple of halfultrasound wavelengths at the nominal center ultrasound frequency.However, the rear HTC layer 102 will be too thick having a thickness oftoo many multiples of the one half wavelength if an undesirable amountof acoustic energy from the rearward ultrasound 107 b is absorbed by therear HTC layer as the rearward ultrasound is being reflected. In someimplementations a single half wavelength thickness is used as acompromise between a too thick heat sink that would absorb too muchacoustic energy and a too thin heat sink that would not remove enoughthermal energy.

The rear HTC layer 102 has high thermal conductivity such as provided byaluminum or other metal-based material (much higher than piezoelectricmaterial, such as at least greater than 100 W/mC for implementations) toenable its use as a thermal pathway for extracting the heat from thepiezoelectric element 104 directly to the rear medium 101 (such as air).Also, using air or other substance with a similar acoustic impedance forthe rear medium 101 allows the rearward ultrasound 107 b to be mostlyreflected as the reflected ultrasound 107 c.

The front HTC section 106 is to be positioned adjacent to the frontmedium 18 so that the combined ultrasound 107 will travel through thefront HTC section 106 on into the front medium 18. The firstimplementation of the transducer 100 further includes a heat sink 108that is thermally coupled to and substantially extending along theillustrative Y-dimension away from the rear HTC layer 102, coupled toand extending along the illustrative Y-dimension away from thepiezoelectric element 104, and coupled to and extending along theillustrative Y-dimension away from the front HTC section 106 to increaseeffectiveness of heat removal from the piezoelectric element 104 whilestaying out of direct travel of the ultrasound 107 along theillustrative X-dimension so as not to diminish ultrasound levelsreaching the front medium 18. As depicted below, although otherimplementations of the heat sink 108 include various segmentation, theheat sink 108 remains out of travel of the ultrasound 107 along theillustrative X-dimension. In general, thermal paths with large thermalgradients are used to draw heat rapidly away from the piezoelectricelement 104 to one or more heat sinks, which are typically relativelylarge masses (several times that of the piezoelectric element 104) ofthermally conductive material.

The heat sink 108 can take the form of a fluid, such as water(circulating or stationary) and/or a solid material including housingstructures (for example, as housing 108 a shown below in FIG. 8) of thethermally enhanced ultrasonic transducer 100. Heat removal can befurther enhanced by active cooling of the heat sink 106 such as by othercirculating water or air through or around a solid version of the heatsink. For instance, water can be circulated through the front HTCsection 106 of the transducer; for smaller heat removal requirements,air can be used, which can be more desirable since air has lesscontamination concerns and generally can have less practical obstaclesto implement than when water is used. Once the heat is removed from thefront HTC section 106, the heat is further removed from the circulatingfluid through use of one or more heat sinks to transfer heat from thefluid to surrounding air.

In implementations one or more portions or instances of the heat sink108 are located in peripheral locations out of the path of the forwardultrasound 107 a, rearward ultrasound 107 b, reflected ultrasound 107 cand the combined ultrasound 107. The rear HTC layer 102 and/or the frontHTC section 106 can be press-fit, and/or bonded using thermallyconductive adhesive, and/or soldered, and/or integrally formed withother structures like a housing portion of the thermally enhancedultrasonic transducer 100 such as aluminum.

In some implementations the front HTC section 106 is thermally coupledbut electrically isolated to the heat sink 108 such as a housingstructure of the thermally enhanced ultrasonic transducer 100 so thatthe housing structure can also be thermally coupled and electricallycoupled to the face of the piezoelectric element facing the rear medium101 or coupled to the rear HTC layer 102 without creating an electricalshort circuit. Alternatively, the front HTC section 106 may be bothelectrically and thermally coupled to the heat sink 108 and the rear HTClayer 102 may be thermally coupled and electrically isolated from theheat sink 108. Generally, thermal coupling is of a sufficient heat fluxto prevent significant elevation of temperature and to preventconsequential diminished ultrasound output. In other words, thermalpathways used to remove heat can scale to the amount of heat generatedby the piezoelectric element 104 so that if heat output increases thethermal pathways have reserve capacity to remove the increases ingenerated heat.

A first variation of the first implementation of the thermally enhancedultrasound transducer 100 is shown in FIG. 8 in which the rear HTC layer102, the piezoelectric element 104, and the front HTC section 106 areall curved to allow for focusing of the combined ultrasound 107 at afocal point 107 e.

A second implementation of the thermally enhanced ultrasound transducer100 is shown in FIG. 9 in which the rear HTC layer 102, thepiezoelectric element 104, and the front HTC section 106 are eachthermally coupled to different instances of the heat sink 108.

A first variation of the second implementation of the thermally enhancedultrasound transducer 100 is shown in FIG. 10 in which only the rear HTClayer 102 is directly coupled to an instance of the heat sink 108.Although this implementation is depicted with the piezoelectric element104 as being round in shape, other implementations of the thermallyenhanced ultrasound transducer 100 have other geometric shapes includingrectangular and elliptical.

In this first variation, heat from the piezoelectric element 104 and thefront HTC section 106 is transferred through the rear HTC layer 102 onto the instance of the heat sink 108 that is directly coupled to therear HTC layer. Furthermore, in this first variation, the rear HTC layer102, the piezoelectric element 104, and the front HTC section 106 aresubstantially spherically or semi-spherically shaped to allow forfocusing of the combined ultrasound 107 having a beam pattern with thefocal point 107 e. Other implementations use focusing schemes such asthe piezoelectric element 104 being aspherically shaped and/or with anacoustic lens applied in front of the piezoelectric element.

A second variation of the second implementation of the thermallyenhanced ultrasound transducer is shown in FIG. 11 in which only thefront HTC section 106 is directly coupled to an instance of the heatsink 108. In this second variation, heat from the rear HTC layer 102 andthe piezoelectric element 104 is transferred through the front HTCsection 106 on to the instance of the heat sink 108 that is directlycoupled to the front HTC section. Furthermore, in this second variation,the rear HTC layer 102, the piezoelectric element 104, and the front HTCsection 106 are all semi-spherically formed as curved to allow forfocusing of the combined ultrasound 107 with respect to the focal point107 e.

A third variation of the second implementation of the thermally enhancedultrasound transducer is shown in FIG. 12 in which the rear HTC layer102 integrated with an instance of the heat sink 108 and the front HTCsection 106 is integrated with another different instance of the heatsink 108. The rear HTC layer 102 and the front HTC section 106 aredirectly integrated with different instances of the heat sink 108 toremain electrically isolated from one another. In this third variation,the piezoelectric element 104 is not directly thermally coupled to aninstance of the heat sink 108. Instead, heat 109 a from thepiezoelectric element 104 is transferred through the rear HTC layer 102as heat 109 b and heat 109 c through the front HTC section 106 as heat109 d on to the instances of the heat sink 108.

A third implementation of the thermally enhanced ultrasound transducer100 is shown in FIG. 13 in which the rear HTC layer 102 and the frontHTC section 106 are thermally coupled to an instance of the heat sink108 and the piezoelectric element 104 is thermally coupled to adifferent instance of the heat sink.

A first variation of the third implementation of the thermally enhancedultrasound transducer 100 is shown in FIG. 14 in which the rear HTClayer 102 is thermally and electrically coupled directly to an instanceof the heat sink 108 and the front HTC section 106 is thermally coupledto the instance of the heat sink through an electrical isolator 109 toremain electrically isolated from one another. In this first variation,heat from the piezoelectric element 104 is transferred through the rearHTC layer 102 and through the front HTC section 106 on to the instanceof the heat sink 108.

A fourth implementation of the thermally enhanced ultrasound transducer100 is shown in FIG. 15 in which the rear HTC layer 102 and thepiezoelectric element 104 are both thermally coupled to an instance ofthe heat sink 108. Also, the front HTC section 106 is thermally coupledto another different instance of the heat sink 108.

A fifth implementation of the thermally enhanced ultrasound transducer100 is shown in FIG. 16 in which the rear HTC layer 102 is thermallycoupled to an instance of the heat sink 108. Also, the piezoelectricelement 104 and the front HTC section 106 are both thermally coupled toanother different instance of the heat sink 108.

A first version of the front HTC section 106 is shown in FIG. 17 ashaving a first front HTC layer 110, an acoustic lens 112, and a secondfront HTC layer 114. Both the first front HTC layer 110 and the secondfront HTC layer 114 can be approximately as thick as one or morequarters of a wavelength near the nominal center frequency of theoperational ultrasound. For example, for a ceramic version of thepiezoelectric element 104 having an acoustic impedance of 34 MRayls anda tissue version of the front medium 18 having an acoustic impedance of1.6 MRayls, some implementations of the first front HTC layer 110 andthe second front HTC layer 114 each of a quarter wave thickness have anacoustic impedance in the range 4 to 10 MRayls. The first front HTClayer 110 and the second front HTC layer 114 can be constructed frommagnesium with an acoustic impedance of 10 MRayls or an epoxy filledwith a thermally conductive material to yield an acoustic impedance ofapproximately 7 MRayls.

The acoustic lens 112 is positioned between the first front HTC layer110 and the second front HTC layer 114. The acoustic lens 112 can alsobe constructed from a high thermal conductivity material (such as in therange of 200-400 W/mC) and assist in removing heat away from thepiezoelectric element 104. As discussed below, the acoustic lens 112 maybe utilized without one or both of the first front HTC layer 110 and thesecond front HTC layer 114, however, generally heat removal from thepiezoelectric element 104 can be greater if one or both of the first HTClayer and the second front HTC layer are used in conjunction with an HTCconstructed acoustic lens.

Additional factors involved with whether to combine the first front HTClayer 110 and/or the second front HTC layer 114 with the acoustic lens112 may depend at least in part on acoustic impedances associated witheach component and the front medium 18 regarding transducer efficiency.In some implementations the acoustic lens 112 can be made from aluminumwith a high thermal conductivity of approximately 237 W/mC. As discussedfurther below, the acoustic lens 112 can be bonded directly to thepiezoelectric element 104 or the first front layer HTC 110. As shown,the combined ultrasound 107 passes through the first front HTC layer110, then passes through the acoustic lens 112, and finally passesthrough the second front HTC layer 114.

A first variation of the fifth implementation of the thermally enhancedultrasound transducer 100 is shown in FIG. 18 as using the first versionof the front HTC section 106.

A second version of the front HTC section 106 is shown in FIG. 19 ashaving the first front HTC layer 110 adjacent to the acoustic lens 112.As shown, the combined ultrasound 107 passes through the first front HTClayer 110 and then passes through the acoustic lens 112.

A second variation of the fifth implementation of the thermally enhancedultrasound transducer 100 is shown in FIG. 20 as using the secondversion of the front HTC section 106.

A third version of the front HTC section 106 is shown in FIG. 21 ashaving the acoustic lens 112 and the second front HTC layer 114. Asshown, the combined ultrasound 107 passes through the acoustic lens 112and then passes through the second front HTC layer 114.

A third variation of the fifth implementation of the thermally enhancedultrasound transducer 100 is shown in FIG. 22 as using the third versionof the front HTC section 106.

A fourth version of the front HTC section 106 is shown in FIG. 23 ashaving the first front HTC layer 110. As shown, the combined ultrasound107 passes through the first front HTC layer 110.

A fifth version of the front HTC section 106 is shown in FIG. 24 ashaving the acoustic lens 112. As shown, the combined ultrasound 107passes through the acoustic lens 112.

A fourth variation of the fifth implementation of the thermally enhancedultrasound transducer 100 is shown in FIG. 22 as using the fifth versionof the front HTC section 106.

Implementations of the thermally enhanced ultrasound transducer 100 canalso include enhancements to the piezoelectric element 104 to increasethermal conduction within the piezoelectric element. Bulk thermalconductivity of the piezoelectric element 104 can be increased byforming a composite matrix of thermal conductive material (such as someepoxies and/or epoxies mixed with high thermal conductivity materialsuch as metals) and piezoelectric material (such as ceramics).

Bulk piezoelectric element thermal conductivity can also be increased byinterleaving ceramic material (such as ceramics) with thermallyconductive layers (such as metals). Effective distances can beconsequently shortened within the piezoelectric element 104 from ceramicmaterial within the piezoelectric element to thermal conductive pathwayswithin the piezoelectric element coupled to one or more thermalconductive pathways and/or one or more instances of the heat sink 108external to the piezoelectric element. External thermal conductivepathways can include the rear HTC layer 102 and the front HTC section106. Thermal conductive pathways internal to the piezoelectric element104 can conduct heat away from piezoelectric material to variousexternal surfaces of the piezoelectric element, external thermalconductive pathways, and one or more instances of the heat sink 108.

A first high thermal conductivity (HTC) implementation of thepiezoelectric element 104 is shown in FIG. 26 as having piezoelectriclayers 116 (such as ceramic) interleaved between high thermalconductivity (HTC) layers 118 (such as metallic electrode material). TheHTC layers 118 are shown bent in a serpentine fashion to thermallycouple together more than one of the HTC layers. The thermallyconductive pathways of the HTC layers 118 can be oriented substantiallynormal to the illustrative X-dimension along the illustrativeY-dimension and parallel to the surfaces of the piezoelectric element104 with the electrode material 104 a.

Since the electrode material 104 a also has a high thermal conductivity,it may also be used as remove heat from the piezoelectric element 104using configurations discussed herein to prevent electrical shorting ofthe piezoelectric element. Methods to construct the first HTCimplementation of the piezoelectric element 104 and otherimplementations include laminate construction similar to that used formultilayer ceramic capacitors and can be used with slip-castpiezoelectric ceramic. In some implementations, a sufficient number ofthe piezoelectric layers 116 are used to produce enough acoustic energyfor the combined ultrasound 107 with the thickness of each of thepiezoelectric layers being much thinner than when the piezoelectricelement is one piece.

Consequently, the first HTC implementation of the piezoelectric element104 can have relatively short distances involved from interior locationsof the piezoelectric layers 116 to thermal pathways such as provided bythe HTC layers 118. The HTC layers 118 can then be thermally coupled toone or more instances of the heatsink 108 such as within housingstructures of the thermally enhanced ultrasound transducer 100. Whencomposed of electrically conductive materials, such as metal, the HTClayers 118 could also be electrically coupled together in series and/orparallel arrangements depending on the electrical properties for an HTCimplementation of the piezoelectric element 104. For example,electrically conductive versions of the HTC layers 118 that areelectrically coupled together in series will reduce the overallelectrical capacitance of a particular HTC implementation of thepiezoelectric element 104, whereas electrically conductive versions ofthe HTC layers that are electrically coupled together in parallel willincrease the overall electrical capacitance of a particular HTCimplementation of the piezoelectric element 104.

A second HTC implementation of the piezoelectric element 104 is shown inFIG. 27 as having multiple of the HTC layers 118 coupled to HTC sidemembers 120 extending perpendicularly to the HTC layers. Whereas thefirst HTC implementation of the piezoelectric element 104 is depicted inFIG. 26 as having two of the piezoelectric layers 116, the second HTCimplementation of the piezoelectric element is depicted in FIG. 27 ashaving five of the piezoelectric layers 116. Other HTC implementationsof the piezoelectric element 104 can have various other numbers of thepiezoelectric layers 116 depending upon such factors as capacity of eachof the piezoelectric layers to produce ultrasound and requirement foramount of ultrasound energy to be produced.

A sixth implementation of the thermally enhanced ultrasound transducer100 is shown in FIG. 28 as using a third HTC implementation of thepiezoelectric element 104 and also using a plano-concave version of theacoustic lens 112. The third HTC implementation uses laminated portionsof the piezoelectric material 116 and the HTC layers 118, which can alsobe electrically conductive. The HTC side members 120 of thepiezoelectric element 104 are positioned adjacent to side portions of ahousing 122, which serve as at least one of the heat sinks 108. The HTClayers 118 also can be thermally coupled directly to back portions ofthe housing 124 for further removal of heat from the piezoelectricelement 104.

A seventh implementation of the thermally enhanced ultrasound transducer100 is shown in FIG. 29 as using a fourth HTC implementation of thepiezoelectric element 104 and also using the plano-concave version ofthe acoustic lens 112. The fourth HTC implementation of thepiezoelectric element 104 has a internally positioned HTC member 126that effectively divides the HTC layers 118 into smaller active elementsto shorten thermal pathways to remove heat from the layers of thepiezoelectric material 116. Other versions of the seventh implementationof the thermally enhanced ultrasound transducer 100 can also include therear HTC layer 102 and/or front HTC section 106 discussed above. Theinternally positioned HTC member 126 is coupled to the back portion ofthe housing 124 as one of the heat sinks 108 for further removal of heatfrom the piezoelectric element 104.

The third and fourth HTC implementations of the piezoelectric element104 include versions of the HTC layers 118 that can be electricallyconductive either coupled to or also serving the function of theelectrode material 104 a. The HTC layers 118 are thermally coupled tostructural components of the thermally enhanced ultrasound transducer100, which also act as instances of the heat sink 108. In addition, heatextraction from the piezoelectric element 104 can be further enhanced bydivision of the piezoelectric layers 116 and the HTC layers 118 intosmaller individual components such as through the use of one or moreinstances of the internally positioned HTC member 126 to further shortenthermal pathways from the piezoelectric layers 118 to one or moreinstances of the heat sink 108.

Other implementations of the thermally enhanced ultrasound transducer100 use the rear HTC layer 102 and/or other implementations of the frontHTC section 106 to aid the removal of heat from the HTC implementationsof the piezoelectric element 104.

A first conventional composite implementation of the piezoelectricelement 14 is shown in FIG. 30 as having first piezoelectric members 128as posts of piezoelectric ceramic. In the depicted version, the firstpiezoelectric members 128 extend along the illustrative X-dimension inwhich the combined ultrasound 107 propagates. A polymer material 130,such as epoxy, is positioned between the first piezoelectric members 128to help remove heat away from the first piezoelectric members. The firstconventional composite implementation can be formed, for instance, froma single piece of piezoelectric ceramic cut with a fine dicing saw intwo orthogonal directions leaving a spaced array of the firstpiezoelectric members 128. The polymer material 130 is used to fillbetween the first piezoelectric members 128. Other dicing schemes may beapplied such as dicing in one direction only or by varying spacing anddimensions of the first piezoelectric members 128.

A second conventional composite implementation of the piezoelectricelement 14 is shown in FIG. 31 having second piezoelectric members 132as fine piezoelectric ceramic fibers. Other spacing or sized fibers canbe used in other conventional composite implementations. A conventionalcomposite implementation of the piezoelectric element 14 can be handledin a manner similar to that for a monolithic version. Typically thefirst piezoelectric members 128 and the second piezoelectric members 132account for a range of 25% to 75% (depicted as 25% in FIG. 30 and 65% inFIG. 31) of the total volume of a composite implementation of thepiezoelectric element 14 for operational frequency ranges used.

A fifth HTC implementation of the piezoelectric element 104 is shown inFIG. 32 as having the first piezoelectric members 128 positioned betweenan aggregate HTC thermally conductive material 134. A sixth HTCimplementation of the piezoelectric element 104 is shown in FIG. 33 ashaving the second piezoelectric members 132 positioned between theaggregate HTC material 134. Versions of the aggregate HTC material 134include the polymer material 130 mixed with particles that have highthermal conductivity and are electrically insulating, such as frommaterials including, but not limited to aluminum oxide, aluminumnitride, zinc oxide, sapphire, and diamond. Because of the relativelyclose packing of the first piezoelectric members 128 and/or the secondpiezoelectric members 132, such as on the order of a few microns, heatflow readily occurs to the aggregate HTC material 134 on to other heatdissipating structures such as one or more instances of the heat sink108.

In alternative implementations, high thermal materials 136 areincorporated directly with piezoelectric material 138, as shown in FIG.34, to form monolithic HTC versions of the piezoelectric element 104,and the piezoelectric material 116, the first piezoelectric members 128,and/or the second piezoelectric members 132. The high thermal materials136 as thermally conductive, electrically insulating powder can beincorporated by custom blending with the piezoelectric material 138 aspiezoelectric ceramic powder prior to firing.

The high thermal materials 136 include, but not limited to, aluminumoxide, aluminum nitride, zinc oxide, sapphire, and diamond. Particlesize of the high thermal materials 136 can be in the range of 20 to 200microns which are large relative to the particles of the piezoelectricmaterial 138 (which typically are a few microns or less in diameter) andsmaller than the thickness of a typical version of the piezoelectricelement 104, and the piezoelectric material 116, the first piezoelectricmembers 128, and/or the second piezoelectric members 132. Relativelylarge particle sizes for the high thermal materials 136 are chosen sothat the interfaces between the fine grain particles of thepiezoelectric material 138 remain and piezoelectric performance ismaintained. Large particle sizes for the high thermal materials 136 havethe further advantage of increased heat transfer.

From the foregoing it will be appreciated that, although specificembodiments of the invention have been described herein for purposes ofillustration, various modifications may be made without deviating fromthe spirit and scope of the invention. For instance, for reasonsincluding ease of illustration, rectangular and plano-concave shapeswere used for depicted implementations; however, other implementationscan use other shapes while staying with the spirit and scope of theinvention. Accordingly, the invention is not limited by only thoseimplementations described in detail herein.

1. A high intensity focused ultrasound transducer for transmittingultrasound toward a front medium along a first dimension, the ultrasoundhaving a first frequency of greater than 100 KHz and less than 10 MHz,the ultrasound of the first frequency having a first wavelength, thetransducer comprising: a rear medium; a rear high thermal conductivitylayer having a thermal conductivity of at least 100 W/mC; apiezoelectric element configured to generate the ultrasound of at least100 KHz; and a front high thermal conductivity section having at leastone member having a thermal conductivity of at least 100 W/mC, the rearmedium, the rear high thermal conductivity layer, the piezoelectricelement, and the front high thermal conductivity section injuxtaposition along the first dimension.
 2. The high intensity focusedultrasound transducer of claim 1 further including a heat sink, the heatsink coupled to the rear high thermal conductivity layer and extendingout of the way of transmission of the ultrasound along the firstdimension, the heat sink coupled to the piezoelectric element andextending out of the way of transmission of the ultrasound along thefirst dimension, and the heat sink coupled to the front high thermalconductivity section and extending out of the way of transmission of theultrasound along the first dimension.
 3. The high intensity focusedultrasound transducer of claim 1 further including a first heat sink, asecond heat sink, and a third heat sink, the first heat sink coupled tothe rear high thermal conductivity layer and extending out of the way oftransmission of the ultrasound along the first dimension, the secondheat sink coupled to the piezoelectric element and extending out of theway of transmission of the ultrasound along the first dimension, and thethird heat sink coupled to the front high thermal conductivity sectionand extending out of the way of transmission of the ultrasound along thefirst dimension.
 4. The high intensity focused ultrasound transducer ofclaim 1 further including a first heat sink and a second heat sink, thefirst heat sink coupled to the rear high thermal conductivity layer andextending out of the way of transmission of the ultrasound along thefirst dimension, and the second heat sink coupled to the piezoelectricelement and extending out of the way of transmission of the ultrasoundalong the first dimension.
 5. The high intensity focused ultrasoundtransducer of claim 1 further including a first heat sink, and a thirdheat sink, the first heat sink coupled to the rear high thermalconductivity layer and extending out of the way of transmission of theultrasound along the first dimension, and the third heat sink coupled tothe front high thermal conductivity section and extending out of the wayof transmission of the ultrasound along the first dimension.
 6. The highintensity focused ultrasound transducer of claim 1 further including asecond heat sink, and a third heat sink, the second heat sink coupled tothe piezoelectric element and extending out of the way of transmissionof the ultrasound along the first dimension, and the third heat sinkcoupled to the front high thermal conductivity section and extending outof the way of transmission of the ultrasound along the first dimension.7. The high intensity focused ultrasound transducer of claim 1 furtherincluding a first heat sink, the first heat sink coupled to the rearhigh thermal conductivity layer and extending out of the way oftransmission of the ultrasound along the first dimension.
 8. The highintensity focused ultrasound transducer of claim 1 further including asecond heat sink, the second heat sink coupled to the piezoelectricelement and extending out of the way of transmission of the ultrasoundalong the first dimension.
 9. The high intensity focused ultrasoundtransducer of claim 1 further including a third heat sink, the thirdheat sink coupled to the front high thermal conductivity section andextending out of the way of transmission of the ultrasound along thefirst dimension.
 10. The high intensity focused ultrasound transducer ofclaim 1 wherein the rear high thermal conductivity layer has a thermalconductivity equal to the thermal conductivity of one of the followingmaterials: gold, pure synthetic diamond, silver, bronze, and aluminum.11. The high intensity focused ultrasound transducer of claim 1 whereinthe rear high thermal conductivity layer is semi-spherically shaped. 12.The high intensity focused ultrasound transducer of claim 1 wherein therear high thermal conductivity layer is aspherically shaped.
 13. Thehigh intensity focused ultrasound transducer of claim 1 wherein the atleast one member of the front high thermal conductivity section issemi-spherically shaped.
 14. The high intensity focused ultrasoundtransducer of claim 1 wherein the at least one member of the front highthermal conductivity section is aspherically shaped.
 15. The highintensity focused ultrasound transducer of claim 1 wherein the at leastone member of the front high thermal conductivity section includes afirst high thermal conductivity layer.
 16. The high intensity focusedultrasound transducer of claim 1 wherein the at least one member of thefront high thermal conductivity section includes a first high thermalconductivity layer.
 17. The high intensity focused ultrasound transducerof claim 1 wherein the at least one member of the front high thermalconductivity section includes an acoustic lens.
 18. The high intensityfocused ultrasound transducer of claim 1 wherein the at least one memberof the front high thermal conductivity section includes a first highthermal conductivity layer and an acoustic lens in juxtaposition. 19.The high intensity focused ultrasound transducer of claim 1 wherein theat least one member of the front high thermal conductivity sectionincludes a first high thermal conductivity layer and a second highthermal conductivity layer in juxtaposition.
 20. The high intensityfocused ultrasound transducer of claim 19 wherein the at least onemember of the front high thermal conductivity section further includesan acoustic lens positioned between the first high thermal conductivitylayer and the second high thermal conductivity layer.
 21. The highintensity focused ultrasound transducer of claim 1 wherein the at leastone member of the front high thermal conductivity section includes afirst front high thermal conductivity layer sized in a first thicknessalong the first dimension substantially an odd multiple of a quarter ofthe first wavelength of the ultrasound.
 22. The high intensity focusedultrasound transducer of claim 21 wherein the first thickness of therear high thermal conductivity layer is less than ten of the firstwavelengths of the ultrasound.
 23. The high intensity focused ultrasoundtransducer of claim 21 wherein the first thickness of the rear highthermal conductivity layer is substantially equal to one half of thefirst wavelength of the ultrasound.
 24. The high intensity focusedultrasound transducer of claim 1 wherein the rear high thermalconductivity layer is sized in a first thickness along the firstdimension substantially a multiple of a half of the first wavelength ofthe ultrasound.
 25. The high intensity focused ultrasound transducer ofclaim 24 wherein the first thickness of the rear high thermalconductivity layer is substantially less than ten of the firstwavelengths of the ultrasound.
 26. The high intensity focused ultrasoundtransducer of claim 24 wherein the first thickness of the rear highthermal conductivity layer is substantially equal to one half of thefirst wavelength of the ultrasound.
 27. The high intensity focusedultrasound transducer of claim 1 further including electrode material,the piezoelectric element positioned between a first portion and asecond portion of the electrode material, the first portion of theelectrode material positioned adjacent the rear high thermalconductivity layer, the second portion of the electrode materialpositioned adjacent the front high thermal conductivity section.
 28. Thehigh intensity focused ultrasound transducer of claim 27 wherein thethickness of the first portion of electrode material is less than 10% ofthe first wavelength between the piezoelectric element and the rear highthermal conductivity layer and wherein the thickness of the secondportion of the electrode material is less than 10% of first wavelengthbetween the piezoelectric element and the front high thermalconductivity section.
 29. A high intensity focused ultrasound transducerfor transmitting ultrasound toward a front medium along a firstdimension, the ultrasound having a first frequency of greater than 100KHz and less than 10 MHz, the ultrasound of the first frequency having afirst wavelength, the transducer comprising: a rear medium; a rear highthermal conductivity layer having a thermal conductivity of at least 100W/mC; and a piezoelectric element configured to generate the ultrasoundof greater than 100 KHz and less than 10 MHz, the rear medium, the rearhigh thermal conductivity layer, and the piezoelectric element injuxtaposition along the first dimension.
 30. The high intensity focusedultrasound transducer of claim 29 further including a front layer injuxtaposition with the piezoelectric element.
 31. A high intensityfocused ultrasound transducer for transmitting ultrasound toward a frontmedium along a first dimension, the ultrasound having a first frequencyof greater than 100 KHz and less than 10 MHz, the ultrasound of thefirst frequency having a first wavelength, the transducer comprising: arear medium; a piezoelectric element configured to generate theultrasound of at least 100 KHz; and a front high thermal conductivitysection having at least one member having a thermal conductivity of atleast 100 W/mC, the rear medium, the piezoelectric element, and thefront high thermal conductivity section in juxtaposition along the firstdimension.
 32. The high intensity focused ultrasound transducer of claim31 further including a rear layer in juxtaposition with the rear mediumand the piezoelectric element.